1. Field of the Invention
The present invention relates in general to a cathode ray tube, more particularly, to a cathode ray tube including a mask spring having a modified structure, thereby reducing a cost of manufacture while improving performance of the mask spring.
2. Discussion of the Background Art
FIG. 1 illustrates the structure of a related art cathode ray tube and mask spring.
As shown in FIG. 1, the related cathode ray tube includes a panel 12 having a fluorescent screen 121 formed on an inner surface, a funnel 10 fastened to the panel 12, an electron gun 14 for emitting electron beams, a deflection yoke 16 for deflecting the electron beams emitted from the electron gun, and a shadow mask 18 having a plurality of electron beam passing holes through which selecting colors of the electron beams.
Also, the shadow mask 18 is connected to the mask frame 20, and the mask frame 20 is fastened on the panel 12 by means of a mask spring 30.
With the above structure, when a designated voltage is applied, the electron gun 14 emits electron beams, and these electron beams are deflected by the deflection yoke 16, pass through the electron beam passing holes formed on the shadow mask 18, and eventually collide with the fluorescent screen 121, displaying an image on a screen.
At this time, a part of the electron beams are transmitted through the electron beam passing holes on the shadow mask 18, but the other part of the electron beams collides with the shadow mask 18.
The collision, namely the kinetic energy, of those electron beams generates heat energy that is in turn transferred to the shadow mask 18. As a result, the metallic shadow mask 18 is thermally expanded by the heat energy.
This thermally expanding shadow mask is depicted in FIG. 2.
As shown in the drawing, when the shadow mask 18 undergoes thermal expansion due to the collision with the electron beams, the electron beam passing holes 19 shift from the initial positions (this phenomenon is called a doming phenomenon), so the electron beams are mis-landed deviating from where they are supposed to be landed.
In fact, mis-landing of the electron beams is the major factor of deteriorations in color purity of images. To minimize the mis-landing effect, there needs a counter-reaction against the doming phenomenon.
The mask spring 30 is what performs the counter-reaction against the doming phenomenon. Of course, as mentioned before, the shadow mask not only performs the counter-reaction against the doming phenomenon, but also supports the mask frame 20 to be fastened to the panel 12.
When the shadow mask 18 is thermally expanded because of heat conduction, the mask frame 20 and the mask spring 30 are also thermally expanded. As a result, the positions of the mask frame 20 and mask spring 30 are changed, causing the electron beams to mis-land.
FIG. 3 is a perspective view of the structure of a mask spring to which a mask frame is attached, and FIG. 4 is a plan view of a mask spring.
Referring to FIGS. 3 and 4, the mask spring 30 includes an fastening portion 31 that is welded to the mask frame 20, a attaching portion 35 that is incorporated with a stud pin formed inside the panel, and a connecting portion 33 that connects the fastening portion 31 with the attaching portion 35.
The fastening portion 31 and the connecting portion 33 are tilted at a designated angle from a bending portion 32, and the attaching portion 35 and the connection portion 33 are tilted at a designated angle from another bending portion 34.
Especially, some of criteria that manufacturers are very careful with when they choose proper materials for the mask frame 20, the shadow mask 18 and the mask spring 30 are thermal characteristics, strength and cost of manufacture. In general, the mask frame 20 is made of iron (Fe), the shadow mask 18 is made of an Fe—Ni alloy having a relatively low thermal expansion coefficient, and the mask spring 30 is made of stainless steel together with an Fe—Ni alloy.
Besides the doming phenomenon aforementioned, there is another phenomenon called a howling phenomenon where the shadow mask 18 is vibrated caused by external impacts or vibrations of a speaker. To minimize the howling of the shadow mask, manufacturers made the mask spring 30 thinner to make it absorb external impacts better.
However, if the thickness of the mask spring 30 is reduced, the counter-reaction effect of the mask spring against the doming phenomenon becomes weak, and particularly the mask spring is not able to withstand external shocks (i.e. drop characteristic) as it used to be.